Field of the Invention
The present invention relates to a Continuous Variable Valve Timing (CVVT) apparatus for an engine, and, more particularly, to an intermediate phase CVVT technique for fixing a phase of a CVVT apparatus in a specific state in an operating region in which a valve timing is not actively adjusted.
Description of Related Art
When an engine is driven in an Atkinson cycle, compression work may be reduced and thus fuel efficiency may be improved. A CVVT apparatus is utilized to realize the Atkinson cycle in a typical Otto-cycle engine.
That is, when the closing of an intake valve in a conventional Otto-cycle engine is delayed using a CVVT apparatus, compared to that in a typical engine, a compression stroke, in which energy for compressing air is consumed when a piston moves toward a top dead point, is practically decreased. Thus, the compression work of the engine may be relatively reduced compared to when the intake valve is not closed due to a delay, so that fuel efficiently may be improved.
However, since the CVVT apparatus is generally operated by hydraulic pressure produced using the power of the engine, it is difficult to actively control the CVVT apparatus when the engine is started.
In addition, when a valve timing is not actively controlled by the CVVT apparatus in the operating region during the idling of the engine, it is advantageous to fuel efficiency since energy consumption is rather small.
Accordingly, the CVVT apparatus is in a default state in which the CVVT apparatus is not actively controlled when the engine is started and idles.
In the engine equipped with the CVVT apparatus, which is configured to adjust the phase of an intake camshaft enough to realize the Atkinson cycle, when the default state is formed in which the CVVT apparatus is not actively controlled by hydraulic pressure, the CVVT apparatus is maintained in the most delayed state by resistance to driving of the intake camshaft. In this case, since the intake valve is delayed and closed in the most delayed state, there is a lack of compression pressure, resulting in faulty starting of the engine and poor combustion during the idling of the engine.
Therefore, it is necessary to fix the CVVT apparatus in the state in which the intake valve timing of the typical Otto-cycle engine is realized, for example so as to be suitable for the engine, in the operating region, in which the CVVT apparatus is not actively controlled, such as in the operating region when the engine is started or idles. To this end, there is disclosed an intermediate phase CVVT apparatus including a locking pin and a locking groove, which fix the phase of a rotor relative to a housing of the CVVT apparatus in a proper state by elastic force even though no hydraulic pressure for controlling the CVVT apparatus is supplied.
The information disclosed in this Background of the Invention section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.